ISSUE FOCUS 32 FEED & ADDITIVE MAGAZINE March 2025 TRYPTOPHAN AND PRODUCTIVE PERFORMANCE OF LAYING HENS The requirement of tryptophan in laying hens may vary depending on several factors: age of the birds, nutritional composition of the diet, especially in relation to the concentration of long-chain neutral amino acids; mathematical models adopted in the studies; feed consumption; genetic lineage and others, so tryptophan recommendations for laying hens ranging from 0.15 to 0.23% are observed (Khattak et al., 2019; Mousavi et al., 2018; Dong et al., 2017; Rostagno et al., 2017; Peganova et al., 2003; Harms & Russel 2000; Coon & Zhang, 1999; NRC, 1994). Studies carried out by Kattak & Helmbrecht (2019) and Peganova et al. (2003) demonstrate high laying rates, 97% and 84%, respectively, through supplementation of L-tryptophan in the diet. Wen et al. (2019) and Cardoso et al. (2014), evaluating different genetic strains and older hens, they observed a high laying rate, 81 and 94%, respectively, by adding L-Tryptophan in the diet. The highest egg production rate found by Cardoso et al. (2014) can be explained by the high level of tryptophan in the diet (Table 1). Cardoso et al. (2014) determined the digestible tryptophan:lysine ratio (Trp: Lys) equal to 25.44% for maximum egg production in white Dekalb laying hens from 60 to 76 weeks of age, using a quadratic polynomial model. Meanwhile, the Hendrix Manual (2020) recommends Trp: Lys ratio equal to 22% in the same period. Rostagno et al. (2017) recommend a ratio of 23% for white and brown laying hens in the egg production phase. Katthak & Helmbrecht (2019) evaluated increasing levels of digestible tryptophan (0.10 to 0.31%) in a corn and wheat-based diet for brown laying hens in the period of peak laying and observed an increase of 2.7% in the feed inGenetic Strain Age, weeks dig. Trp Mathematical model Effect Reference Lohmann Brown Lohmann Brown White laying hens Dekalb White Dekalb Brown Lohmann Brown Hy-Line W36 Hy-Line W36 Peganova et al. (2003) Peganova et al. (2003) Lima et al. (2012) Cardoso et al. (2014) Moreira et al. (2018) Khattak & Helmbrecht (2019) Wen et al. (2018) Sarsour et al. (2021) 31-37 31-37 29-49 60-76 44-68 22-28 41-46 22-34 0.15% 0.18% 0.19% 0.19% 0.20% 0.25% 182.3 mg/day 183 mg/day Improved egg mass Improved egg mass Improved egg mass Improved egg mass Improved egg shell thickness Improved egg production Improved egg production Improved egg production Table 1. Tryptophan levels and effects on production parameters in laying hens. Broken-Line Exponential Quadratic Quadratic Quadratic Linear Quadratic Broken-Line Quadratic Broken-Line
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